.net - 如何在不违反 MVVM 原则的情况下处理拖放？

Question

目前我在我的 XAML

<TabControl  
    AllowDrop="True"
    PreviewDragOver="DragOver"
    PreviewDrop="Drop" />

我所有的拖放代码都存在于我的 View 的代码隐藏中，而不是我的 ViewModel 中。

如何在 ViewModel 中处理拖放而不在 View 上添加任何依赖项？

Answer 1

这是我编写的一些代码，允许您在不违反 MVVM 的情况下将文件拖放到控件上。它可以很容易地修改为传递实际对象而不是文件。

/// <summary>
/// IFileDragDropTarget Interface
/// </summary>
public interface IFileDragDropTarget
{
    void OnFileDrop(string[] filepaths);
}

/// <summary>
/// FileDragDropHelper
/// </summary>
public class FileDragDropHelper
{
    public static bool GetIsFileDragDropEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsFileDragDropEnabledProperty);
    }

    public static void SetIsFileDragDropEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsFileDragDropEnabledProperty, value);
    }

    public static bool GetFileDragDropTarget(DependencyObject obj)
    {
        return (bool)obj.GetValue(FileDragDropTargetProperty);
    }

    public static void SetFileDragDropTarget(DependencyObject obj, bool value)
    {
        obj.SetValue(FileDragDropTargetProperty, value);
    }

    public static readonly DependencyProperty IsFileDragDropEnabledProperty =
            DependencyProperty.RegisterAttached("IsFileDragDropEnabled", typeof(bool), typeof(FileDragDropHelper), new PropertyMetadata(OnFileDragDropEnabled));

    public static readonly DependencyProperty FileDragDropTargetProperty =
            DependencyProperty.RegisterAttached("FileDragDropTarget", typeof(object), typeof(FileDragDropHelper), null);

    private static void OnFileDragDropEnabled(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue == e.OldValue) return;
        var control = d as Control;
        if (control != null) control.Drop += OnDrop;
    }

    private static void OnDrop(object _sender, DragEventArgs _dragEventArgs)
    {
        DependencyObject d = _sender as DependencyObject;
        if (d == null) return;
        Object target = d.GetValue(FileDragDropTargetProperty);
        IFileDragDropTarget fileTarget = target as IFileDragDropTarget;
        if (fileTarget != null)
        {
            if (_dragEventArgs.Data.GetDataPresent(DataFormats.FileDrop))
            {
                fileTarget.OnFileDrop((string[])_dragEventArgs.Data.GetData(DataFormats.FileDrop));
            }
        }
        else
        {
            throw new Exception("FileDragDropTarget object must be of type IFileDragDropTarget");
        }
    }
}

用法:

<ScrollViewer AllowDrop="True" Background="Transparent" utility:FileDragDropHelper.IsFileDragDropEnabled="True" utility:FileDragDropHelper.FileDragDropTarget="{Binding}"/>

确保 DataContext 继承自 IFileDragDropTarget 并实现 OnFileDrop。

public class MyDataContext : ViewModelBase, IFileDragDropTarget
{
    public void OnFileDrop(string[] filepaths)
    {
        //handle file drop in data context
    }
}